Typically, an elastic electric contact terminal on which soldering is possibly performed is required to have a good electric conductivity, a good elastic recovery force, and a high tolerance to a soldering temperature.
As an example of the elastic electric contact terminal, Korean Patent No. 783588 registered by the present applicant discloses a solderable elastic electric contact terminal including: an insulation foam rubber having a constant volume; an insulation non-foaming adhesive layer adhered to wrap the insulation foam rubber; and a heat-resistant polymer of which one side is adhered to wrap the insulation non-foaming adhesive layer and the other side on which a metal layer is integrally formed.
In addition, Korean Patent No. 1001354 discloses a reflow solderable elastic electric contact terminal including: an insulation elastic heat-resistant rubber core in which a penetration hole is formed in a longitudinal direction; an insulation heat-resistant adhesive layer adhered to wrap the insulation heat-resistant rubber core; and a heat-resistant polymer film of which one side is adhered to wrap the insulation heat-resistant adhesive layer and the other side has an integrally formed metal layer, wherein the heat-resistant polymer film is adhered to the insulation heat-resistant adhesive layer such that both ends are separated and a bottom surface of the insulation elastic heat-resistant rubber core is obliquely formed in a shape that both ends in a transverse direction is grooved toward a central part.
In the above-described process of fabricating the electric contact terminal, a rolled silicon rubber is provided, a liquid silicon rubber adhesive is consecutively placed thereon in a longitudinal direction of the silicon rubber, a polymer film in which a metal layer is formed is wrapped to expose the metal layer outside on the liquid silicon rubber adhesive, and then the silicon rubber adhesive is cured to adhere to the polymer film. Then the resultant is cut to a uniform length of, for example, 500 mm and cut again in a length of, for example, 3 mm required by a customer. Thereafter the resultant product plated with a metal is reel-taped.
Here, the metal layer is formed by plating a copper foil with tin or silver or plating a copper foil with nickel and then with tin or gold thereon, and the thickness of the copper foil is about 0.01 mm, which is significantly thicker than that of tin, silver, nickel or gold.
In this way, a metal plating layer of which environmental resistance is better than that of copper is formed on a copper foil of an existing contact terminal such that corrosion is prevented and soldering with a solder cream is well performed, but during a process for fabricating the contact terminal, the contact terminal is cut off to a length required by a customer. Therefore, the copper foil is only to be exposed outside at a cross section formed on a side in a longitudinal direction of the contact terminal.
In other words, since an existing contact terminal is made by wrapping a core in a polymer film having a copper foil plated with a metal layer such as tin and then is cut off, the copper foil is only to be exposed outside at the cross section.
As a result, there occurs a limitation in that the contact terminal may not pass a reliability test such as a saltwater spray test, since saltwater contacts the externally exposed copper foil to corrode the contact terminal, or in that the externally exposed copper foil is easily rusted to result in quality degradation.
In addition, there is a shortcoming that when the contact terminal is reflow-soldered to be mounted on a circuit board, since the copper foil is exposed at an externally exposed cross section, a lead-rising phenomenon occurs less on the copper foil than on the metal plating layer, which results in a less strong soldering strength at the cross section.
In addition, since the copper foil wrapping and adhering to the polymer film is bended at both bottom ends of the core, the bended copper foil always receives an elastic recovery force caused by an attempt to return to an original position, although the magnitude is small. There is also a limitation in that when the contact terminal is mounted on a circuit board by reflow-soldering, the melted soldering cream is applied to the copper foil to pull the copper foil downward and the pulling force is added to the elastic recovery force of the copper foil itself, thereby both ends of the polymer film being detached from the core or the adhesive.
Similarly, it is highly possible that both end parts of the polymer film are lifted and detached from the core or the adhesive before the adhesion is completed, when the polymer film and core are adhered with the adhesive in a making process.